1. Technical Field
The present invention relates generally to devices used for positioning b ocal and trifocal segments on the lenses of corrective eyewear, and more particularly to such devices that rest on a table top and on which the person being fitted for new glasses rests their chin, yet are lightweight and easily moved from one location to another.
2. Background Information
A very large segment of the population wears corrective eyewear to aid a variety of vision problems. Many of these people need assistance with focusing on both distant and close objects For those people, corrective eyewear having bifocal lenses and sometimes trifocal lenses may be necessary. The specially ground portion of the lens containing the bifocal or bifocal and trifocal segment, which is intended more particularly to help in viewing nearby objects, is known generally as the multifocal segment. In order for the multifocal segment to provide the greatest assistance to the person wearing the eyewear, while minimizing the amount of interference with distant viewing, the multifocal segment must be precisely positioned on the lens.
Certain instruments and techniques have been developed and incorporated into what have become known as "conventional methods" for properly positioning the multifocal segment on an eyeglass lens. Among these methods is the use of a millimeter ruler held in the hand of the dispenser, the person who fits the eyewear on the patient, the person who is being fitted for eyewear. Using this method, as with any method of positioning the multifocal segment on the eyeglass lenses, it is important that the dispenser have available the frames that the patient has selected, and that the frames already be properly fitted to the patient. The dispenser places the frames on the patient, and then measures the distance from the bottom of the lens for rimless frames, or the bottom of the frame eyewire, to the location on the patient with which the upper edge of the multifocal segment should be aligned. For visible bifocal lenses, the dispenser measures to where the eyelashes grow from underneath the patient's eye. For no-line bifocal lenses, the dispenser measures to the center of the patient's pupil. For trifocal lenses, the dispenser measures to just below the pupil. This measurement is recorded for each eye, and the distance measured determines the position on the lens for locating the upper edge of the multifocal segment.
There are several potential sources for inaccuracy in this method. It is very important when using this method to align properly the millimeter ruler to make accurate measurements, and many dispensers become quite proficient at this. However, there are many circumstances when even the most able dispensers have difficulty keeping their measurements accurate. For example, an elderly patient may become fatigued from maintaining their head in an upright position while the dispenser makes the appropriate measurements. Likewise, a patient with Parkinson's disease may not be able to maintain a steady head position with any amount of effort. The dispenser may also become while trying to make an accurate measurement and trying to adopt to the peculiar problems a patient may have with holding their head steady. If there is a height disparity between the patient and the dispenser, the measurements also may be adversely affected by the dispenser's attempt to look directly at the face of the patient, if in fact the dispenser does not adequately compensate for the height difference. Some patients are not comfortable with having a ruler held close to their face, right in front of their eyes, and may flinch, shake or otherwise make the measurements very difficult to take with accuracy. Measurement taken in this way may also be time-consuming since it is frequently necessary to double-check dimensions if the patient's head is moving.
Other devices have been developed for measuring these distances. U.S. Pat. No. 4,055,900 for a DEVICE FOR MAKING OPTHALMIC [sic] MEASUREMENTS AND METHOD, issued to Grolman et al. on Nov. 1, 1977, discloses a device fitted to the frames selected by the patient, the whole assembly then being fitted to the face of the patient. The device, while capable of making relatively accurate measurements, is heavy, and may slide down the nose of the patient, distorting the measurements taken by the dispenser. Similarly, U.S. Pat. No. 4,653,192 for a SEGMENT HEIGHT MEASURING DEVICE, issued to Conrad et al. on Mar. 31, 1987, and U.S. Pat. No. 4,494,837 for a PUPIL LOCATION GAUGE, issued to Bommarito on Jan. 22, 1985, also disclose a device that is fitted to the frames selected by the patient Although lighter in weight than the device of Grolman et al., these devices also require the dispenser to be positioned directly perpendicular to the eyes of the patient to take an accurate measurement. However, if the device is too heavy or uncomfortable for the patient, especially an elderly patient or one suffering from Parkinson's, as described-above, it may be difficult if not impossible to maintain the patient's head in the proper position for accurately determining the needed dimensions.